My guess is based off misconceptions people have (like what I bolded), these sites have started to change their marketing strategy. The latest commercials are showing people playing their uncles...or around a table at a restaurant playing their friends. These sites don't play you....you don't lose to them. They just hold your money and score your matchup. So you can play strangers or your office mates.
They simply take 5%...or whatever the rake is... and payout the rest. No stake on the outcome, they get paid either way...no mafia behind the scenes needed.
Think of it as a casino. These sites are not the blackjack table where players are playing against the house. It's more like the poker room. The dealer doesn't play, just takes a little off every pot.